1. Field of the Invention
The present invention relates to technology to achieve space-saving on a peripheral rim outside the display pixel region of a display device, for example, a liquid crystal display device, an EL (Electronic Luminescent) display device, and the like.
2. Description of the Related Art
There are liquid crystal display devices having a display panel with a liquid crystal film sandwich-sealed between two glass substrates. Display devices with this type of liquid crystal display device have recently come into practical use in which driver elements are mounted on the peripheral rim of the display panel, wherein the peripheral rim refers to the peripheral region outside the display pixel area in one of the two glass substrates that are opposite to each other and moreover outside the coverage area of another of the two glass substrates.
The liquid crystal display device described in JP 3033124, for example, is mounted with a scan line driver element and a signal line driver element in the peripheral rim of the display panel. The scan line driver element has a scan line driver circuit, which is formed on a glass substrate and constituted of thin film transistors. The signal line driver element has a signal line driver circuit, which is formed on a glass substrate and constituted of thin film transistors. FIG. 1 is a perspective view illustrating a configuration of this type of a liquid crystal display device. FIG. 2 is a plain view of part A in FIG. 1. Explanation is next presented regarding the conventional liquid crystal display device based on FIG. 1 and FIG. 2.
This conventional liquid crystal display device is provided with glass substrate 1, glass substrate 2, scan line driver element 3, signal line driver element 4 and FPC (flexible printed circuit) cable 5.
Glass substrate 1 is a quadrangular glass substrate. This glass substrate 1 has: quadrangular display pixel region 2′, which is made up of a plurality of display pixels arrayed in a matrix individually selected by a plurality of scan lines 16 and a plurality of signal lines 17; peripheral rim 1′ that remains which is the area exclusive of display pixel region 2′; scan line electrode column 16′ made up of the ends of a plurality of scan lines 16 provided on one side of display pixel region 2′; and signal line electrode column 17′ made up of the ends of a plurality of signal lines 17 provided on another side of display pixel region 2′ adjoining the side on which scan line electrode column 16′ is provided.
Glass substrate 2 is a quadrangular glass substrate arranged in the position opposite to glass substrate 1 across the liquid crystal layer (not shown) to serve for display pixel region 2′.
Scan line driver element 3 is structured to have a scan line driver circuit (not shown) formed on quadrangular glass substrate 54 to supply a voltage to scan lines 16.
Signal line driver element 4 is structured to have a signal line driver circuit (not shown) formed on quadrangular glass substrate 54′ to supply a voltage to signal lines 17.
FPC cable 5 is a quadrangular cable adapted to connect the present liquid crystal display device and an external circuit. FPC cable 5 transfers the signals such as control signals, a clock signal, etc. and power supply voltages to scan line driver element 3 and signal line driver element 4 from the external circuit.
The conventional liquid crystal display device can be explained as described below by defining the long side of a quadrangle as a length and the short side as a width.
Peripheral rim 1′ includes a peripheral rim along scan line electrode column 16′ and a peripheral rim along signal line electrode column 17′. The width W3 of FPC cable 5 is wider than the width W1 of peripheral rim 1′ along scan line electrode column 16′ and narrower than the width W2 of the peripheral rim along signal line electrode column 17′. Signal line driver element 4 is mounted on the peripheral rim along signal line electrode column 17′. Scan line driver element 3 and FPC cable 5 are mounted on the peripheral rim along scan line electrode column 16′. The length of scan line driver element 3 and the width of FPC cable 5 are in the same direction as the length of scan line electrode column 16′. The width W5 of glass substrate 1 substantially equals the sum of the length L1 of scan line driver element 3 (nearly equal to the length of scan line electrode column 16′) and the width W3 of FPC cable 5.
More detailed explanation is hereinbelow given regarding the conventional liquid crystal display device.
The display panel of this conventional liquid crystal display device is configured to have glass substrate 1 and glass substrate 2 in opposite positions across a liquid crystal layer.
On the surface of glass substrate 1, there are formed a plurality of thin film transistors (not shown) for applying a voltage to the display pixel electrodes, a plurality of scan lines 16 each for electrically selecting one of the columns of a plurality of the thin film transistors, and a plurality of signal lines 17 orthogonally intersected with scan lines 16 and each for electrically selecting one of the columns of a plurality of the thin film transistors. On the surface of glass substrate 2, there are formed the electrodes (not shown) opposite to the display pixel electrodes.
On one side of glass substrate 1, there is provided scan line electrode column 16′, in which a plurality of scan line electrodes are aligned. On another side adjoining the side on which scan line electrode column 16′ is provided, there is provided signal line electrode column 17′, in which a plurality of signal line electrodes are aligned.
Scan line driver element 3 is mounted on peripheral rim 1′ on the side of glass substrate 1 on which scan line electrode column 16′ is provided. In scan line driver element 3, output terminals 18 of the scan line driver circuit are aligned to connect to each of the corresponding scan line electrodes of scan line electrode column 16′ on glass substrate 1. Likewise, signal line driver element 4 is mounted on peripheral rim 1′ on the side of glass substrate 1 on which signal line electrode column 17′ is provided. In signal line driver element 4, output terminals 20 of the signal line driver circuit are aligned to connect to each of the corresponding signal line electrodes of signal line electrode column 17′ on glass substrate 1.
On the edge of one end of glass substrate 54 of scan line driver element 3, there are formed input terminals 19, and likewise, on the edge of one end of glass substrate 54′ of signal line driver element 4, there are formed input terminals 21. These input terminals 19, 21 are connected to FPC cable 5 in a corner of glass substrate 1 by means of solder etc. Further, in the corner of glass substrate 1, there are aligned connection terminals 22, 23 to be electrically connected to FPC cable 5.
A problem encountered in this conventional liquid crystal display device, however, has been that it is impossible to shorten the size of the width of the peripheral rim where the signal line driver element is mounted. This problem originates from the size of the width of the signal line driver element. The reason for this is as described below.
With the recent development of new techniques, the width of a scan line driver element has been narrowed to not greater than 4 mm, but a signal line driver element requires from ten to several hundred times the number of transistors that are needed for the scan line driver element in.
In addition, the two-system power supply wiring and GND wiring are required for the power supply conductor to be wired within the signal line driver element. Now, it is assumed that the two-system power supply wiring and GND wiring are wired within a 30 cm long signal line driver element. For example, if it is presumed that the wiring in each system of the two-system power supply is a 1 mm thick copper wiring through which 50 mA electric current flows, then, it is necessary to set the wiring width of each power supply wiring to 2.5 mm or greater in order to limit the voltage drop across the power supply wirings in the signal line driver element to 0.1 V or lower, allowing for a specific resistance of a copper wire of 1.7×10−8 Ωm. Further, if it is presumed that current of 100 mA flows through the GND wiring, which is a copper wiring of 1 mm in thickness through which 100 mA electric current flows, then, it is necessary to set the wiring width of the GND wiring to 5 mm or wider in order to limit the voltage drop across the GND wiring in the signal line driver element to 0.1 V or lower.
For this reason, only the wiring widths of the power supply wirings in the signal line driver element attain 10 mm or wider (each of the widths of the power supply wirings of the two systems being 2.5 mm and the width of GND line being 5 mm). As a result, it is impossible as a matter of course to have the signal line driver element 4 mm wide or less as with the scan line driver element.
Consequently, it is necessary to increase the size of the width of the peripheral rim to mount the signal line driver element, because the width of the signal line driver element attains 10 mm or wider.